The present invention relates to the field of medical prostheses and a two-stage surgical implantation of same to replace a defective joint, such as a hip joint.
Surgical techniques have heretofore existed for the implantation of prosthesis in humans and animals to replace diseased, defective, or damaged portions of the anatomy, such as the various articulating joints of the body. For a number of years medical procedures have been employed for the implantation of a porous prosthesis, after which, bony tissues reforms in porosities of the implant to anchor same within a prepared bone cavity. In similar fashion, prostheses have been surgically implanted utilizing polymeric cement compositions. The cement composition is forced into a prepared bone cavity, after which the prosthesis is properly positioned within the cavity, surrounded by the cement, with the joint component of the prosthesis being properly located in the acetabulum cavity or the like. In situ curing of the cement composition then secures the prosthesis stem within the cavity. A more recent implantation technique has utilized a prosthesis precoated with a cementitious composition similar to the bone cement composition that is to be utilized during the implant procedure. The precoat is cured in vitro to provide a generally pore-free, outer polymer surface which then bonds to the bone cement in situ during implantation to provide improved implant fixation. A significant development effort has also been expended in the area of prosthesis design.
In general, certain problems or disadvantages accompany all current implantation techniques. In particular, prostheses implanted with bone cement are subject to failure after a number of years due to stress fractures across the bone-cement-prosthesis interfaces. Should failure occur, it becomes necessary to remove the prosthesis, and to repeat the procedure, both of which are undesirable to the patient and are quite problematical in success. Tissue ingrowth fixation techniques alluded to above, have heretofore involved a one-step surgical procedure in which the bone canal adjacent a joint is reamed to define an appropriate opening, the bone joint, per se, is resectioned and a one or two-piece prosthesis is surgically implanted. A prolonged postoperative period is necessary to permit bone tissue ingrowth into porosities of the prosthesis before the joint can be utilized or, specifically with regard to the hip joint, before the patient may become ambulatory. Such prolonged patient immobilization is highly undesirable and susceptible to cause disuse muscle atrophy, permanent or temporary reduction of joint function, bone resorption, and general degeneration of patient health. The likelihood of such consequences has generally, negated the employment of bone ingrowth fixation procedures on elderly patients, or other patients where prolonged immobilization would be highly undesirable.
The method and product according to the present invention overcome the disadvantages noted above with respect to prior techniques of implantation, particularly implantation of a prosthetic hip joint. Specifically, after a first surgical technique in which only a stem portion of the prosthesis is implanted, the patient may return to an ambulatory condition very quickly since the joint is not affected. Indirect loading of the stem during normal mobility, accelerates dynamic bony interfacial fixation with the stem, preferably bone ingrowth into porosities in the stem and improves the interfacial strength of same with the stem. After suitable interfacial fixation has occurred, the joint is surgically approached and the joint removed while exposing the tip of the previously implanted stem. Thereafter, a prosthetic joint component is inserted and secured to the implanted stem tip. Upon completion of the second surgical technique and a postoperative recuperative period, the prosthesis may be directly loaded. Consequently, the procedure of the present invention may be practiced on elderly patients. The general consequences of the prior prolonged periods of immobilization are vastly diminished if not alleviated, while increasing the speed of rehabilitation and improving interfacial strength between the prosthesis and the bone.
The prior art is devoid of any teaching or suggestion of the procedure or prosthesis of the present invention. Exemplary of the prior art are:
U.S. Pat. No. 3,708,805, PA1 U.S. Pat. No. 3,864,758, PA1 U.S. Pat. No. 3,924,275, PA1 U.S. Pat. No. 4,051,559, PA1 U.S. Pat. No. 4,187,559, PA1 U.S. Pat. No. Re 28,895, PA1 G.B. Pat. No. 1,334,584 PA1 Ger. Pat. No. 2,411,617.